In recent years, a method of manufacturing electronic devices using ink-jetting techniques has been calling attention.
Compared to vapor deposition or other process, ink-jetting facilitates inexpensive manufacture using equipment with a simple structure. Further, because ink-jetting is a direct patterning technique, masks are not required unlike in vapor deposition and thus manufacture of larger products is possible. For example, as demands of the market for larger displays in electronic display devices have increased, expectations for a technique for manufacturing electronic devices by ink-jet coating have also increased.
A manufacturing technique by coating will be described below using an organic EL display panel as an example.
FIG. 1 shows a structure of an organic EL display panel. The organic EL display panel includes substrate 1, cathodes 32, light emitting layers 301R, 301G and 301B, anodes 33, and partition walls (hereinafter also referred to as “banks”) 31. Substrate 1 includes TFTs (not shown) for driving the display inside. Further, a seal film, a color filter, or the like (not shown) are appropriately arranged over cathode 32.
The organic EL display panel includes three types of light emitting layers corresponding to three colors: red (R), green (G) and blue (B). The three-color light emitting layers are represented by 301R, 301G and 301B. Banks 31 are used for the patterning of ink to be applied to each pixel, in ink-jet coating that will be described in the following section of a manufacturing process. Ink refers to a solution containing a material of a light emitting layer dissolved in solvent.
Examples of the raw material of the light emitting layer of the organic EL display panel include polymeric materials such as polyfluorenes, polyarylenes, polyarylenevinylenes, alkoxybenzene and alkylbenzene, and examples of the solvent include toluene, xylene, acetone, anisole, methyl ethyl ketone, methyl isobutyl ketone, cyclohexylbenzene and mixed solvent thereof.
Because bank 31 is formed to define a region in which ink is to be applied, ink that has been applied remains in the desired pixel region. By this means, a high-quality display can be manufactured without causing mixing of inks among pixel regions. A fluorine-containing resin is used as a material of bank 31. Bank 31 is ink repellent.
The device thus configured emits a light when electrons from the cathode and holes from the anode are combined in the light emitting layer, consequently performing a function as a display.
FIG. 2 shows a cross-section of the organic EL display panel cut at the height of the light emitting layer. FIG. 2 shows an example in which three colors of R, G and B are patterned in the form of pixel. By making each of the pixels emit a light, the organic EL display panel can function as a display apparatus for a TV or the like. A region in which the pixels are formed is called a display region.
The width of the pixel and the pixel pitch is 50 to 100 μm. Because the width of the pixel and pixel-to-pixel distance are extremely small, precise coating techniques such as ink jetting is required.
Next, a process of manufacturing the organic EL display panel will be described.
First, an anode is arranged on the substrate by photolithography.
Next, a bank is made by photolithography. Afterward, inks of R, G and B for the light emitting layer are applied on the substrate by ink-jet printing. The applied inks are dried in the coating step and the subsequent step and a pattern of the light emitting layer is formed. Afterward, a cathode is formed on the light emitting layer by sputtering or the like.
The application of ink by ink-jetting will be described below.
FIGS. 3A and 3B show an overview of an ink-jet apparatus (or droplet ejection apparatus). FIG. 3A shows a state before coating regions are formed on substrate 1 by the ink-jet apparatus. FIG. 3B shows a state after coating regions are formed on substrate 1 by the ink-jet apparatus.
As shown in FIGS. 3A and 3B, the ink-jet apparatus includes mount 41, substrate transfer stage 42 disposed on mount 41, and ink-jet head 50 facing substrate transfer stage 42. Ink-jet head 50 is mounted on gantry 43 disposed across substrate transfer stage 42. Regarding the size of substrate 1, a substrate made of the eighth generation glass is around 2 m×2.5 m.
FIGS. 4A and 4B show a structure of the ink-jet head. FIG. 4A shows a cross-sectional view of the ink-jet head when a pressure is not applied to pressure chamber 110. FIG. 4B shows a cross-sectional view of the ink-jet head when a pressure has been applied to pressure chamber 110.
The ink-jet head includes multiple nozzles 100 for ejecting ink, pressure chambers 110 that communicate with nozzles 100, partition walls 111 that separate pressure chambers 110, diaphragm 112 that constitutes part of pressure chambers 110, piezoelectric elements 130 that vibrate diaphragm 112, piezoelectric elements 140 that support partition walls 111, common electrodes 120 and individual electrodes 121 for applying a voltage to piezoelectric elements 130, and drive circuit 122 to which common electrodes 120 and individual electrodes 121 are connected. The ink-jet head further includes an ink feed port (not shown).
Further, when being configured to circulate ink, the ink-jet head further includes an ink discharge port (not shown). Piezoelectric element 130 and piezoelectric element 140 are formed by cutting a plate of the piezoelectric element material by dicing. Nozzle 100 has a diameter of 20 to 50 μm, and the pitch of nozzle 100 is 100 to 500 μm. The number of nozzles 100 in each row is 100 to 300.
The ink-jet head thus configured operates as follows. When a voltage is applied between common electrode 120 and individual electrode 121, piezoelectric element 130 is deformed from the state shown in FIG. 4A to the state shown in FIG. 4B. When piezoelectric element 130 is deformed, the volume of pressure chamber 110 decreases to apply a pressure to ink. By the pressure, ink is ejected from nozzle 100.
Next, the coating operation of the ink-jet apparatus will be described.
Substrate transfer stage 42 is moved from the state shown in FIG. 3A to the state shown in FIG. 3B. At this time, ink is discharged from ink-jet head 50 toward substrate 1 disposed on substrate transfer stage 42 to apply ink to region 44 on substrate 1 to which ink needs to be applied. The speed at which substrate transfer stage 42 is transferred is 20 to 400 mm/s. The ejection frequency is 1,000 to 5,000 Hz. The ink-jet apparatus forms a pixel pattern by detecting the position of substrate transfer stage 42 and controlling the timing of ink ejection.
In order to form the pixel pattern, it is necessary to reduce the variation in angle at which droplets to be ejected from nozzle 100 is ejected. The maximum allowable value of the variation in ink ejection angle is generally 10 to 50 mrad. A phenomenon in which ink droplets are not ejected straightly from nozzle 100 is generally called “curved flying of ink droplets.” Due to factors such as the accuracy of manufacturing nozzle 100, degradation of liquid-repellent coating of nozzle 100, a remaining ink material after wipe, a variation in ink ejection angle may occur between the early stage and the middle stage when manufacturing a product by a coating method.
A technique for correcting the variation is disclosed in Patent Literature 1, in which piezoelectric elements are provided around nozzles to control the direction for ink ejection. FIG. 5 shows an ink-jet head according to Patent Literature 1. Reference sign 13 denotes a nozzle. Ink is ejected by applying a voltage to piezoelectric element 22 by electrodes 21 and 23 to deform piezoelectric element 22 and vibration plate 18. At the same time, the direction for ink ejection is controlled by deforming thin plate material 16 arranged at the outlet of nozzle 13 by piezoelectric element 22.
Further, an ink-jet apparatus having partition walls that separate pressure chambers, piezoelectric element A for applying a pressure to a pressure chamber via a diaphragm, and piezoelectric element B that is in contact with each partition wall via the diaphragm, is known (for example, see Patent Literatures 2 to 7). Among such apparatus, an ink-jet apparatus is known in which an electrical circuit is connected to both of piezoelectric element A and piezoelectric element B, and when piezoelectric element A is extended toward a pressure chamber, piezoelectric element B is extended or contracted with respect to a pair of partition walls that form this pressure chamber (for example, see Patent Literatures 4 and 5). Alternatively, an ink-jet apparatus is known in which: the width of a part of piezoelectric element A, the part being in contact with the diaphragm in the direction in which nozzles are lined; the width of a part of piezoelectric element B, the part being in contact with the diaphragm; and the width of a part of the partition wall, the part being in contact with the diaphragm; are smaller than the widths of piezoelectric element A, piezoelectric element B, and the partition wall, respectively, and the relationships among the above widths are defined (for example, see Patent Literatures 6 and 7).
In addition to the above apparatus, the following ink-jet apparatus are known: an ink-jet apparatus having partition walls, piezoelectric elements A, and a diaphragm, the partition walls being a laminate of multiple layers having different stiffness (for example, see Patent Literatures 8 and 9); and an ink-jet apparatus having piezoelectric element A and partition walls integrally formed with the ceiling of a pressure chamber, in which extended piezoelectric element A presses the ceiling to deform the partition walls so as to apply a pressure to ink in the pressure chamber (for example, see Patent Literature 10).